1) KB958559-(xXX).msu isn't and update for Windows 7 and you can't find this one on Microsoft Update Catalog! To download the update for Microsoft Virtual PC KB958559-(xXX).msu you need to validate your copy of Windows 7 (Windows Genuine Advantage Validation), even if Windows 7 is already activated! 2) However if you want check if your Windows 7 copy is activated just go to: Control Panel | System And you will see Windows is activated and the Microsoft original Logo! 3) Activation and validation are two differents process! And you need a Windows 7 copy activated to validate this one to download softwares or updates Microsoft Genuine Advantage! Genuine Windows: frequently asked questions Windows Genuine Advantage on Wikipedia I think I haven't made myself clear around here. I use a retail windows 7 home prem, which is registered, activated and validated and is rtlited. I downloaded this update which was last week released by MS and tried it on this windows version. The installation went well, wanted a reboot, but the update couldn't be installed as it is installed after reboot. Windows reverted to earlier state without installation. This is the reason why I want to know the dependency as I have remove just a few things from this version. I will try and find out what really is going amiss to keep this update from installation and I will post my details out here.